add: chaotic-nyx with CachyOS kernel

- Add chaotic-nyx input for access to CachyOS packages
- Import chaotic nixosModules in flake outputs
- Switch from zen kernel to linuxPackages_cachyos
- Enable sched-ext schedulers (scx) for improved scheduling

https://claude.ai/code/session_012fr2N5SNf2LJpy3itB8D8S

configuration.nix

@@ -27,7 +27,8 @@
   # ═══════════════════════════════════════════════════════════════
   boot.loader.systemd-boot.enable = true;
   boot.loader.efi.canTouchEfiVariables = true;
-  boot.kernelPackages = pkgs.linuxPackages_zen;
+  boot.kernelPackages = pkgs.linuxPackages_cachyos;
+  chaotic.scx.enable = true;  # Enable sched-ext schedulers for CachyOS
 
   # ═══════════════════════════════════════════════════════════════
   # NETWORKING